This invention relates to a high speed logic driver circuit, and more particularly to such a driver circuit especially suitable for high density integration. Still more particularly, the present invention is directed to a driver circuit having very low power consumption and controlled output transition times.
Push-pull and open collector driver circuits are widely used in data processing systems, examples of push-pull driver circuits being found in U.S. Pat. No. 4,251,737 issued Feb. 17, 1981 to Gaudenzi, U.S. Pat. No. 4,092,551 issued May 30, 1978 to Howard et al, U.S. Pat. No. 4,071,783 issued Jan. 31, 1978 to Knepper and U.S. Pat. No. 4,016,431 issued Apr. 5, 1977 to Henle et al, all of which are commonly assigned to the assignee of the present application. Examples of open collector driver circuits can be found, for example, in the above-cited U.S. Patent to Gaudenzi and in Mathews et al, SATURATED OFF-CHIP DRIVER FOR LOW-POWER APPLICATION, IBM Technical Disclosure Bulletin, Vol. 17, No. 10, March 1975, page 2920.
In past years, emphasis has been placed on improving the operating speeds of driver circuits. However, in very high-density, low-end master slices, low power dissipation is frequently of greater significance than high speed. Indeed, since most or all of the critical logic paths are on a single chip, all-out performance is usually not necessary. Instead, high input/output (I/O) count and heat removal constraints mandate low power dissipation.
A further troublesome characteristic encountered in many driver circuits is that the output transitions may be too fast, and this creates considerable noise on both off-chip nets and on-chip power distributions. The off-chip noise results in restrictive wiring rules.